In a manufacturing process of a semiconductor device, various films having different physical properties are formed on a silicon substrate and these films are subjected to various processes, thus forming fine metal interconnects. For example, in a damascene interconnect forming process, interconnect trenches are formed in a film, and the interconnect trenches are then filled with metal, such as Cu. Thereafter, an excessive metal is removed by chemical mechanical polishing (CMP), so that metal interconnects are formed.
A CMP apparatus (or a polishing apparatus) for polishing a substrate typically includes an apparatus for cleaning and drying a polished substrate. Cleaning of the substrate is performed by bringing a cleaning tool, such as a roll sponge, into sliding contact with the substrate while rotating the substrate horizontally. After cleaning of the substrate surface, ultrapure water (DIW) is supplied onto the surface of the rotating substrate, thereby rinsing the surface of the substrate. Before the substrate is dried, the ultrapure water is further supplied onto the surface of the rotating substrate to rinse the surface of the substrate.
A chemical liquid, which is supplied for cleaning the substrate, is diluted 30 to 500 times with the ultrapure water. This ultrapure water has been deaerated in advance so that dissolved oxygen is removed from the ultrapure water. Generally, an amount of oxygen dissolved in the ultrapure water is at most 10 ppb, or may be even regulated at 5 ppb or less.
FIG. 15 is a schematic view showing an example of a conventional apparatus for rinsing a substrate by supplying the ultrapure water onto a surface of the substrate. A substrate (or wafer) W is rotated horizontally by chucks (not shown), while the ultrapure water is supplied onto a central portion of the substrate from a tube nozzle 201 which is disposed outside of the substrate W. FIG. 16 shows a schematic view showing another example of a conventional apparatus for rinsing a substrate by supplying the ultrapure water onto a surface of the substrate. In this apparatus, a substrate (or wafer) W is rotated horizontally, while the ultrapure water is sprayed onto a surface of the substrate from a spray nozzle 202 which is disposed outside of the substrate W.
In recent years, copper has been widely used for metal interconnects of devices. It is a known fact that, if the amount of dissolved oxygen is 1000 ppb (1 ppm) or more, the copper (Cu) is likely to be corroded. As described above, although the amount of dissolved oxygen in the ultrapure water is very small, the oxygen in an atmosphere is dissolved in the ultrapure water until the ultrapure water reaches the surface of the substrate when using the conventional apparatus as shown in FIG. 15 and FIG. 16, thus increasing the amount of dissolved oxygen. As a result, the corrosion of the copper interconnects formed on the substrate surface may be accelerated. In particular, the copper interconnects formed on a peripheral portion of the substrate may be rapidly corroded because the peripheral portion of the substrate rotates at a higher velocity.
As one solution for the copper interconnect corrosion, there has been generally known a method using hydrogen water (functional water) that is produced by adding hydrogen into the ultrapure water. However, producing the hydrogen water entails a large-sized equipment, which increases costs. Moreover, in this method also, the hydrogen water is passed through the atmosphere to reach the substrate. Therefore, the oxygen in the atmosphere is dissolved in the hydrogen water, hindering an effect of the hydrogen water that can prevent the copper corrosion. It is possible to avoid such oxygen dissolution if a substrate processing space is filled with an inert gas, such as nitrogen gas. However, the apparatus structure becomes complicated, and the costs may further increase because it is necessary to take a security measure for the consumption and the use of the inert gas.